Known ball valves are controlled by a handle secured to a projection portion of a stem connected to the ball valve and extending exteriorly of the valve body. An abutment flange is secured to the valve handle and abuts a fixed projection which is mounted adjacent the handle portion. When the handle is turned and the flange abuts the stop element or stop post, the handle can no longer be rotated. Accordingly, if it is desired to have the ball valve displaced from a fully closed to a half open position, then it is necessary to position the handle where the ball valve is half-open and then to disconnect the flange which is usually secured by a nut threaded in the end of the stem extending through the handle and to position the flange against the stop post. The nut is then rethreaded so that the stop flange is fixed at an arresting position. Accordingly, when the arm is turned, the stop flange will arrest the handle at the half-open valve position.
A disadvantage of these types of stopper members is that they are time consuming to install, they are not precise and often become loose if the handle is forced to an open position and therefore no longer provide the satisfactory result that it was intended for.